1. Field of the Invention
The present invention relates generally to recording medium transportation apparatus incorporated in an image recording apparatus for example printing an image on a sheet of paper or a similar recording medium. The present invention relates particularly to improved recording medium transportation apparatus employing a belt drive device, with a belt having a surface having a suction force produced by air suction and thus holding a recording medium on the belt to transport the recording medium.
2. Description of the Background Art
Printers and copiers are conventionally known as equipment for example printing an image on a sheet of paper, film or a similar recording medium. Such equipment use a belt drive device as means for transporting a recording medium.
To reliably transport a recording medium on a belt, a recording medium transportation apparatus adopts a configuration adhering the recording medium on the belt. More specifically, a chamber is arranged facing a back surface of the belt. The chamber has a surface facing the belt that is provided with suction holes and it is internally vacuumed to allow the suction holes to provide air suction. Furthermore, the belt is also for example blanked and thus provided with a large number of suction holes. Thus the recording medium is adhered on the belt when a negative pressure is produced in the chamber and each suction hole thus provides air suction. This can prevent the recording medium from displacing on the belt. Thus the recording medium transportation apparatus can reliably transport the recording medium.
However, the transportation apparatus adhering a recording medium on a belt and thus transporting the recording medium cannot provide a uniform negative pressure between the recording medium and the belt. More specifically, that portion of the recording medium close to a suction hole of the belt and therearound adheres to the belt with a large negative pressure, whereas that portion of the recording medium slightly apart from the suction hole of the belt adheres to the belt with an extremely small negative pressure, i.e., the atmospheric pressure. In other words, between the recording medium and the belt a region with an extremely high negative pressure and that with an extremely low negative pressure are alternately provided. As such, the recording medium can disadvantageously have an entire surface receiving a reduced average pressure. Thus the recording medium transportation apparatus does not ensure that it reliably transports the recording medium.
To overcome this disadvantage, Japanese Patent No. 2738532 and Japanese Patent Laying-Open No. 7-304167 disclose transportation apparatus.
The former discloses a transportation apparatus using a belt having a rough surface knurled in a diamond pattern. This can prevent a region of a high negative pressure from existing around a suction hole of the belt. Thus, a uniform negative pressure can act over an entire surface of a recording medium.
The latter discloses a belt formed of a porous film, a meshed sheet or the like to provide a uniform negative pressure over the entirety of an area to be printed.
However, there has not been made any suggestion in optimizing a belt surface roughness to obtain an appropriate action of a negative pressure.
The present inventor has noted a relationship between the force allowing a recording medium to adhere to a belt and the belt""s surface roughness, and, with his findings, as provided hereinafter, the present inventor has studied on optimizing a belt surface roughness.
More specifically, if a belt has too rough a surface, too large a space is created between the belt and a recording medium and thus results in a reduced suction resistance. Thus, the chamber has a reduced negative pressure therein and can thus not provide a sufficient level of force adhering the recording medium to the belt. This would result in a high possibility of the transportation apparatus failing to reliably transport the recording medium. In addition, the fine convexities and concavities of the belt surface can be reflected on a front side or image bearing side of the recording medium. Thus an image cannot be formed on a smooth surface or obtain high quality.
In contrast, if a belt has an insufficiently rough surface, then a region with an extremely high negative pressure and that with an extremely low negative pressure alternately exist between a recording medium and the belt, as has been described above, resulting in a reduced average pressure preventing the transportation apparatus from reliably transporting the recording medium.
As such, in order to ensure a sufficient force allowing a recording medium to adhere to a belt to reliably transport the recording medium it is important to set an optimal belt surface roughness.
In particular, for a transportation apparatus intermittently transporting a recording medium, such as ink jet printers, the recording medium insufficiently adhering to the belt would tend to slide on the belt and an image formed on the recording medium can have a significantly degraded quality. As such, for printers of this type it is particularly important to have an optimized belt surface roughness.
To provide an optimally set belt surface roughness, it is also important to carefully set a distance between adjacent suction holes. That is, setting a distance between adjacent suction holes is also an important factor in reliably transporting a recording medium to form an image of high quality.
The present invention has been made to overcome the above disadvantages and contemplates a recording medium transportation apparatus transporting a recording medium adhered to a belt through air suction, wherein a belt surface roughness and a distance between adjacent suction holes can be optimized to provide a level of force allowing the belt to optimally adhere to the recording medium to transport the recording medium with high precision.
More specifically, the present invention basically provides a recording medium transporting apparatus including a recording medium transporting belt having a suction hole to provide air suction to allow a recording medium to adhere to and thus transported on a surface of the belt. For this recording medium transportation apparatus, an equivalent adhesion diameter (Dx) is represented by:                               0.5          xc3x97                                    D              ⁢                              xe2x80x83                            ⁢              0                        2                    ⁢                      xe2x80x83                    ⁢                      e                          c0              /              c1                                      ≦        Dx        ≦                  0.95          xc3x97                                    D              ⁢                              xe2x80x83                            ⁢              0                        2                    ⁢                      xe2x80x83                    ⁢                      e                          c0              /              c1                                                          (        1        )            
wherein D0 represents a diameter of a suction hole and c0, c1 are each a fitting value (c0=16.49 and c1=6.05), and the aforementioned recording medium transporting belt has a surface roughness (Ra) represented by:                     Ra        =                              {                                                            Dx                                      5                    /                    2                                                  -                                                      (                                          D                      ⁢                                              xe2x80x83                                            ⁢                                              0                        /                        2                                                              )                                                        5                    /                    2                                                                                                c                  ⁢                                      xe2x80x83                                    ⁢                  0                                -                                  c                  ⁢                                      xe2x80x83                                    ⁢                  1                  ⁢                                      xe2x80x83                                    ⁢                  ln                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  2                        ·                                                  Dx                          /                          D                                                                    ⁢                                              xe2x80x83                                            ⁢                      0                                        )                                                                        }                                1            /            3                                              (        2        )            
with Dx substituted by expression (1).
More specifically, when a suction hole has a diameter D0 of 1 to 2 mm, the recording medium transporting belt has a surface roughness Ra set to 1.9 to 13.7 xcexcm.
Furthermore, if a suction hole has a diameter D0 of 2 to 5 mm, the recording medium transporting belt has a surface roughness Ra set to 3.4 to 29.4 xcexcm.
As described specifically as above, a belt can have a surface roughness set as appropriate and thus obtain a level of force acting to allow the belt to adhere to a recording medium satisfactorily. Thus the transportation apparatus can reliably transport the recording medium.
Furthermore, the present invention also has a feature providing a setting as described below, to optimize a distance between a center of a suction hole and that of another suction hole adjacent thereto. More specifically, in a recording medium transporting apparatus similar in configuration to the above described transportation apparatus, with a suction hole having diameter D0 represented by xcex1 and a recording medium transporting belt having surface roughness Ra represented by xcex2, a distance (p) between a center of a suction hole and that of another suction hole adjacent thereto is set to have a dimension of at least Dx with D0 and Ra substituted by xcex1 and xcex2, respectively, in expression (2):                     Ra        =                              {                                                            Dx                                      5                    /                    2                                                  -                                                      (                                          D                      ⁢                                              xe2x80x83                                            ⁢                                              0                        /                        2                                                              )                                                        5                    /                    2                                                                                                c                  ⁢                                      xe2x80x83                                    ⁢                  0                                -                                  c                  ⁢                                      xe2x80x83                                    ⁢                  1                  ⁢                                      xe2x80x83                                    ⁢                  ln                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  2                        ·                                                  Dx                          /                          D                                                                    ⁢                                              xe2x80x83                                            ⁢                      0                                        )                                                                        }                                1            /            3                                              (        2        )            
More specifically, when the suction hole has diameter D0 of 1 to 2 mm, the recording medium transporting belt has surface roughness Ra of 1.9 to 13.7 xcexcm and distance p between the centers of adjacent suction holes has a value set at at least 7.6 mm.
Furthermore, when the suction hole has diameter D0 of 2 to 5 mm, the recording medium transporting belt has surface roughness Ra of 3.4 to 29.4 xcexcm and distance p between the centers of adjacent suction holes has a value set at at least 19.1 mm.
As described specifically as above, a distance between the centers of adjacent suction holes can be set corresponding to at least a maximal distance allowing a negative pressure to act on the entirety of a recording medium. This can prevent adjacent suction holes from being spaced by too small an inter-center distance and thus providing an extremely large hole-to-belt ratio and hence a low negative pressure.
Furthermore, the present invention provides another feature providing the following setting to optimize a belt surface roughness with an inter-center distance between adjacent suction holes considered. More specifically, in a recording medium transportation apparatus similar in configuration to the above described recording medium transportation apparatus, with a suction hole having diameter D0 represented by xcex1 and adjacent suction holes spaced by a distance p, the recording medium transporting belt has surface roughness Ra in a range represented by:                     Ra        =                              {                                                            Dx                                      5                    /                    2                                                  -                                                      (                                          D                      ⁢                                              xe2x80x83                                            ⁢                                              0                        /                        2                                                              )                                                        5                    /                    2                                                                                                c                  ⁢                                      xe2x80x83                                    ⁢                  0                                -                                  c                  ⁢                                      xe2x80x83                                    ⁢                  1                  ⁢                                      xe2x80x83                                    ⁢                  ln                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  2                        ·                                                  Dx                          /                          D                                                                    ⁢                                              xe2x80x83                                            ⁢                      0                                        )                                                                        }                                1            /            3                                              (        2        )            
with D0 and Dx substituted by xcex1 and (0.5xc3x97pxe2x89xa6Dxxe2x89xa6p), respectively.
As described specifically as above, the belt can have a surface roughness set as optimized and thus achieve a level of force allowing the belt to adhere to a recording medium satisfactorily. Thus the transportation apparatus can reliably transport the recording medium.
Furthermore, if suction holes are linked together by a groove the groove has a depth set as below. More specifically, a belt has a surface provided with suction holes adjacent to each other and linked together by a groove having a depth d represented by:                                                         p              2                        ⁢            Ra            ⁢                          xe2x80x83                        ⁢            min                                2            ⁢                          h              ⁡                              (                                  p                  -                  h                                )                                                    ≦        d        ≦                                            p              2                        ⁢            Ra            ⁢                          xe2x80x83                        ⁢            max                                2            ⁢                          h              ⁡                              (                                  p                  -                  h                                )                                                                        (        3        )            
wherein p represents a distance between the centers of adjacent suction holes, h represents a width of the linking groove, Ra max represents a maximal value of a surface roughness of a recording medium transporting belt obtained in expression (2), and Ra min represents a minimal value of a surface roughness of the recording medium transporting belt obtained in expression (2).
As provided specifically as above, if a belt has a relatively small surface roughness, the belt can have a surface with the linking groove provided therein and optimized in depth to achieve a level of force as effectively as a belt having an optimally set surface roughness.
Furthermore, if suction holes are linked together by a groove, the groove has a width set as provided below. More specifically, a belt has a surface provided with suction holes adjacent to each other and linked together by a groove having a width h set in a range as represented by:                                           dp            -                                                                                d                    2                                    ⁢                                      p                    2                                                  -                                  2                  ⁢                                      dp                    2                                    ⁢                  Ra                  ⁢                                      xe2x80x83                                    ⁢                  min                                                                          2            ⁢            d                          ≦        h        ≦                              dp            -                                                                                d                    2                                    ⁢                                      p                    2                                                  -                                  2                  ⁢                                      dp                    2                                    ⁢                  Ra                  ⁢                                      xe2x80x83                                    ⁢                  max                                                                          2            ⁢            d                                              (        4        )            
As provided specifically as above, if a belt has a relatively small surface roughness, it can provide a level of force allowing the belt to adhere to a recording medium as effectively as a belt having an optimally set surface roughness.
Furthermore, a belt has a surface with a coefficient of statical friction optimized, as described below. More specifically, the recording medium transporting belt has a coefficient of static friction of at least 1.0 relative to a recording medium transported thereon.
Setting a relatively high coefficient of statical friction can provide a sufficient level of force allowing the belt to adhere to the recording medium in the horizontal direction to reliably transport the recording medium.
Thus the present invention can provide a recording medium transportation apparatus transporting a recording medium adhered on a belt through air suction, wherein the belt has a surface roughness optimally set to ensure that the belt adheres to the recording medium with an appropriate level of force. More specifically, there is not provided a suction resistance extremely increased to reduce in size a region which a negative pressure acts on (when the belt has too low a level of surface roughness), nor between the belt and the recording medium is there provided a gap extremely large to provide a suction resistance extremely reduced and thus failing to provide a sufficient level of force allowing the belt to adhere to the recording medium (when the belt has too high a level of surface roughness). Thus the transportation apparatus can reliably transport the recording medium and thus allows an image to be formed with high quality. The present invention is particularly effective when it is applied to an image formation apparatus intermittently transporting a recording medium, such as an ink jet printer in which a recording medium readily slides on its belt, since the present invention ensures that the recording medium does not slide on the belt.
Furthermore, the belt does not have too high a level of surface roughness and the belt thus does not have a surface with fine convexities and concavities reflected on a front side of a recording medium. As such, an image can be formed on a smooth surface and hence with high quality.
Furthermore, if adjacent suction holes are spaced by an optimized inter-center distance, the adjacent suction holes are not spaced by too small a distance and they thus do not provide an extremely increased suction hole-to-belt ratio. This can prevent a negative pressure from being weak. This also ensures that the belt achieves an appropriate level of force allowing the same to satisfactorily adhere to a recording medium. Thus the transportation apparatus can reliably transport the recording medium to allow an image to be formed with high quality.
Furthermore, if suction holes are linked together by a groove having a depth and width set as appropriate, a belt having a relatively small level of surface roughness can also achieve a level of force allowing the same to adhere to a recording medium as effectively as a belt having a surface roughness set as appropriate. In other words, while the belt can have a surface roughness set as desired, the recording medium transportation apparatus can reliably transport a recording medium to allow an image to be formed with high quality.
Furthermore, if a belt has a surface with a coefficient of statical friction set to be at least 1.0, it can obtain a sufficient level of force allowing the same to adhere to a recording medium in the horizontal direction. The effect of a coefficient of statical friction of this level, together with an effect of the belt having an optimized surface roughness as above, that of suction holes spaced by an optimized inter-center distance as above and that of the suction hole linking groove having optimized dimensions in width and depth as above, ensures that the transportation apparatus reliably transports a recording medium.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.